1. Field of the Invention
The invention relates generally to systems for separating water from hydrocarbons (e.g. oil) in a well and in particular to methods and apparatus for monitoring and controlling a downhole oil/water separator.
2. Prior Art
In an oil well, a quantity of water left from "well completion" or from "water flooding" is mixed with the oil during production and both fluids flow to the surface from underground formations. The water is typically separated at the surface and then injected back into the underground formations. As the water-oil ratio (WOR) increases, the cost of operating the well increases. Much of the cost is in managing the ever increasing volumes of water that must be lifted to the surface, separated, treated, pipelined and injected back into the formations. As the WOR increases, the profitability of the well is diminished until it is no longer economically possible to continue production. This often results in leaving large amounts of oil in place in the formation.
The excessive cost of separating water from oil at the surface of a well has lead to downhole separation systems. U.S. Pat. No. 5,269,153 discloses a downhole separation system which is shown in FIG. 1. The well 13 comprises a downhole oil/water separation system including a cyclone separator 11 having a separation chamber 15 wherein liquids of different densities are separated. Mixed liquids enter through inlet 17 at a high tangential speed so as to generate the required centrifugal force for subsequent separation and pass into separation chamber 15. A first outlet 19 is provided for liquids having a first density and a second outlet 21 is provided for liquids having a second density. A stream of mainly oil flows out of outlet 19 and along recovery conduit 27. A steam of mainly water passes through outlet 21 into disposal conduit 33 and is injected into the formation through injection perforations 34.
While downhole separation systems have improved well performance, there is a need in the art for improved downhole oil/water separation systems. In particular, there is a need for downhole oil/water separation systems that can monitor parameters downhole and control the downhole oil/water separator based on monitored parameters so as to achieve the proper separation and to optimize the performance of the separator. This is well appreciated when the feed entering the separator varies in properties such as oil and water viscosity which depends strongly on temperature and more importantly the water-oil ratio.